Prepreg and diaphragm

Abstract

To provide a prepreg which enables manufacture of a laminated diaphragm without using an adhesive, and a diaphragm using the prepreg.SOLUTION: A prepreg having a carbon fiber and an impregnation resin, wherein the impregnation resin is a thermoplastic resin containing acid-modified polypropylene, and the carbon fiber is a cloth (woven) material. A diaphragm 3 can be produced by laminating a prepreg 2 on at least one surface of a foam 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a prepreg and a diaphragm. [Background technology]

[0002] 2. Description of the Related Art Speakers used in mobile devices, electronic devices, etc. are provided with a diaphragm for converting electrical signals into sound waves. Patent Document 1 describes a diaphragm for a loudspeaker that has a main body containing polyamide 6 or polyamide 66 and polypropylene to enhance heat resistance, and an edge portion formed around the periphery of the main body from a sea structure of polypropylene and an island structure of cross-linked ethylene propylene diene rubber.

[0003] Patent Document 2 describes a speaker diaphragm that contains a carbon fiber filler inside a dicyclopentadiene resin with the aim of reducing weight and enabling mass production. In this case, the carbon fiber is a filler that can be injected into an injection mold and flow with the resin.

[0004] Patent Document 3 describes a speaker diaphragm made of a thermoplastic resin film layer and an inorganic fiber layer to which a thermosetting resin is attached. Examples of the inorganic fiber include carbon fiber, the thermoplastic resin includes polyamide, and the thermosetting resin includes epoxy resin.

[0005] Patent Document 4 describes a speaker diaphragm made of polyamide resin reinforced with a fiber reinforcement material, and cites carbon fiber cloth as an example of the fiber reinforcement material. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-82744 [Patent Document 2] Japanese Patent Application Publication No. 2018-157285 [Patent Document 3] Japanese Patent Application Laid-Open No. 62-109497 [Patent Document 4] Japanese Patent Application Publication No. 1-229600 Summary of the Invention [Problem to be solved by the invention]

[0007] As diaphragms become smaller and lighter, composite structures in which foam is laminated onto elastic materials have been proposed. However, conventional composite structures require adhesives to bond the foam to the elastic material, which increases manufacturing costs. Furthermore, from an environmental perspective, adhesives used must comply with VOC regulations and be outgassing-free.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a prepreg that can be used to fabricate a laminated diaphragm without using an adhesive, and a diaphragm that uses the prepreg. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention provides a prepreg having carbon fibers and an impregnating resin, wherein the impregnating resin is a thermoplastic resin containing acid-modified polypropylene.

[0010] The thermoplastic resin may contain 40% by weight or more of acid-modified polypropylene. The carbon fibers may have a diameter of 5 to 18 μm. The carbon fiber has a fiber weight of 40 to 250 g / m 2 The carbon fiber layer may be formed as follows. The carbon fibers may be continuous fibers. The carbon fibers may be UD (unidirectional) material or cross (woven) material. The Vf value, which is the volume ratio of the carbon fibers in the prepreg, may be 35% or more.

[0011] The prepreg may be a prepreg for a diaphragm.

[0012] The present invention also provides a diaphragm comprising a foam body and the prepreg laminated on at least one surface thereof. [Effects of the Invention]

[0013] According to the present invention, by using a prepreg made by impregnating carbon fiber with a thermoplastic resin containing acid-modified polypropylene, the adhesive properties of the acid-modified polypropylene can be utilized to laminate the prepreg onto a foam. Furthermore, because the prepreg uses carbon fiber as the impregnated base material, it has a high elastic modulus and rigidity. By combining carbon fiber and acid-modified polypropylene, a prepreg for a diaphragm can be provided that has a high sound wave propagation velocity, low density, and high internal loss. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a diaphragm using a prepreg. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described below based on preferred embodiments.

[0016] The prepreg of the embodiment is a prepreg having carbon fibers and an impregnating resin, and is characterized in that the impregnating resin is a thermoplastic resin containing acid-modified polypropylene, thereby obtaining a prepreg suitable for a diaphragm.

[0017] An example of a diaphragm using a prepreg according to an embodiment is shown in Fig. 1. Diaphragm 3 shown in Fig. 1 has prepregs 2 laminated on both sides of foam 1 in the thickness direction.

[0018] The diaphragm 3 has four important physical properties: (1) a high bending modulus, (2) a high bending rigidity, (3) a low density, and (4) a large internal loss.

[0019] Flexural modulus (Pa) is E, density (kg / m 3 ) is ρ, and the speed of sound propagating through the medium (m / s) is V, then V = (E / ρ) 1 / 2 For example, the speed of sound in air is approximately 340 m / s, but in polystyrene (PS) it is approximately 2400 m / s, in iron it is approximately 6000 m / s, in aluminum it is approximately 6400 m / s, and in carbon fiber reinforced plastic (CFRP) it is approximately 6000 to 6500 m / s.

[0020] Therefore, the higher the elastic modulus and the lower the density, the faster the sound speed and the better the vibration characteristics. Furthermore, if the diaphragm is not strong enough and has a low elastic modulus, sound quality may deteriorate in the high-pitched range. If the internal loss (tan δ) is moderately large, the kinetic energy that deforms the diaphragm is released as heat energy, making it easier for vibrations to be damped and suppressing amplitude.

[0021] The prepreg of the embodiment uses carbon fiber as the fiber substrate to be impregnated with the thermoplastic resin. The carbon fiber may be any material obtained by carbonizing organic fiber while it is in a fibrous state by heating. The organic fiber used as the raw material for the carbon fiber may be polyacrylonitrile (PAN) or a spinning pitch obtained by spinning pitch. In other words, the carbon fiber may be a PAN-based carbon fiber made primarily from PAN, or a pitch-based carbon fiber made primarily from spinning pitch.

[0022] The diameter of the carbon fibers is preferably smaller than the thickness of the prepreg, and may be, for example, 5 to 18 μm. The average diameter of the carbon fibers may be within a range of 5 to 18 μm. The average diameter may be calculated as the number average of the diameters of the carbon fibers cut perpendicular to the length direction. Carbon fibers with an appropriate diameter facilitate impregnation with a thermoplastic resin and can produce a prepreg with high elasticity and rigidity.

[0023] The carbon fibers are preferably continuous fibers. The length direction of the continuous fibers is preferably aligned substantially perpendicular to the thickness direction of the prepreg. The continuous fibers may be single fibers or filaments composed of multiple single fibers. The carbon fibers may be UD (unidirectional) material or cross (woven) material.

[0024] When the carbon fibers are UD (unidirectional) materials, the carbon fibers may be aligned in the same direction throughout the entire thickness of the prepreg, or may have a cross-ply structure in which the carbon fibers are aligned in the same direction in each layer in the thickness direction, with the carbon fibers in different layers laminated so as to cross each other.

[0025] When the carbon fiber is a cloth (woven) material, the carbon fibers crossing each other vertically and horizontally are woven by switching the top and bottom in a predetermined manner. The woven structure of the fabric is not particularly limited, and examples thereof include plain weave, twill weave, and satin weave.

[0026] A spread sheet obtained by processing a filament composed of many single fibers to have a small number of fibers in the thickness direction and a wide width is suitable as an impregnation substrate. Methods for spreading fiber bundles include squeezing the fiber bundles with a round rod-shaped jig, dispersing the fiber bundles by applying a water or air current, and dispersing the fiber bundles by irradiating them with ultrasonic waves.

[0027] In the prepreg of the embodiment, the impregnating resin (matrix) impregnated into the carbon fiber is a thermoplastic resin. The thermoplastic resin used in the prepreg of the embodiment contains acid-modified polypropylene.

[0028] The proportion of acid-modified polypropylene in the thermoplastic resin is preferably 40% by weight or more, and may be 70% by weight or more, 80% by weight or more, 100% by weight, etc. When a thermoplastic resin other than acid-modified polypropylene is used in combination, a thermoplastic resin that is compatible with acid-modified polypropylene is preferred, such as polypropylene.

[0029] The polypropylene (PP) may be a propylene homopolymer (homo PP), a propylene-ethylene copolymer (random PP), or a block copolymer (block PP), or may be a copolymer of propylene and another vinyl monomer. Examples of the other vinyl monomer include ethylene, 1-butene, isobutylene, 1-hexene, and α-olefins, and the like, used alone or in combination of two or more. Preferably, 51% by weight or more of the monomers contained in the acid-modified polypropylene are propylene.

[0030] In consideration of the flexural modulus characteristics of the prepreg, the melting point of the acid-modified polypropylene is preferably 120°C or higher and 200°C or lower, more preferably 135°C to 170°C, and even more preferably 140°C to 150°C. Even when impregnated with acid-modified polypropylene having a melting point of less than 120°C, the flexural modulus of the prepreg is unlikely to increase. Impregnation of carbon fibers with acid-modified polypropylene having a melting point of more than 200°C is difficult. Specific examples of melting points include the melting point of Admer (registered trademark) QF551 (manufactured by Mitsui Chemicals, Inc.) of 135°C, the melting point of QE060 of 140°C, the melting point of QF580 of 145°C, and the melting point of QF550 of 165°C.

[0031] The method for producing the acid-modified polypropylene is not particularly limited, but it may be a graft copolymer obtained by grafting an acidic functional group-containing monomer onto unmodified polypropylene using a radical polymerization initiator. An acidic functional group-containing monomer may also be used as the other vinyl monomer to be copolymerized with propylene. Examples of the radical polymerization initiator include organic peroxides and aliphatic azo compounds.

[0032] Examples of the acidic functional group-containing monomer include α,β-unsaturated carboxylic acid monomers such as acrylic acid, methacrylic acid, maleic acid, nadic acid, fumaric acid, itaconic acid, citraconic acid, crotonic acid, and tetrahydrophthalic acid, and unsaturated dicarboxylic acid anhydride monomers such as maleic anhydride, nadic anhydride, itaconic anhydride, and citraconic anhydride. In the acid-modified polypropylene, one type of acidic functional group-containing monomer may be used, or two or more types may be used in combination. Maleic anhydride-modified polypropylene is particularly preferred.

[0033] The proportion of the acidic functional group-containing monomer contained in the acid-modified polypropylene (modification rate) is, for example, 0.01 to 10% by weight, and more preferably 0.05 to 2.5% by weight. The modification rate can be calculated by quantifying the acidic functional groups contained in the acid-modified polypropylene by infrared absorption spectroscopy, nuclear magnetic resonance spectroscopy, titration, or the like, and then taking into account the molecular weight of the acidic functional group-containing monomer. In quantifying the acidic functional groups, the acidic functional groups may be detected directly, or other functional groups derived from the acidic functional groups may be detected.

[0034] The acid-modified polypropylene preferably has physical properties suitable for impregnation and adhesion. The molecular weight of the acid-modified polypropylene is not particularly limited, but may be, for example, about 100,000 to 1,000,000.

[0035] The thermoplastic resin to be used as the impregnating resin may contain desired additives other than the resin. Examples of additives include heat stabilizers, light stabilizers, antioxidants, lubricants, release improvers, colorants, flame retardants, plasticizers, silane coupling agents, antistatic agents, surfactants, nucleating agents, antiblocking agents, weather resistance agents, neutralizing agents, inorganic fillers, and rubber components. These additives may be used alone or in combination of two or more.

[0036] The prepreg of the embodiment is impregnated with a thermoplastic resin containing acid-modified polypropylene, which provides excellent adhesiveness and facilitates secondary processing. It is preferable that the prepreg does not contain a thermosetting resin such as an epoxy resin. Because the acid-modified polypropylene has adhesive properties, it is not necessary to use a curable material such as an adhesive, but such a material may be used as long as it does not affect performance or subsequent processes. Because the acid-modified polypropylene is a thermoplastic resin, when processing the prepreg, the acid-modified polypropylene is softened or melted by heating, allowing repeated adhesion to be achieved.

[0037] One method for impregnating a carbon fiber substrate with a thermoplastic resin is to laminate a film of thermoplastic resin on the substrate and then heat press the laminate. The thermoplastic resin is softened or melted by the heat press and penetrates into the gaps between the carbon fibers, thereby impregnating the carbon fiber with the thermoplastic resin.

[0038] When spread fibers made of spread carbon fiber bundles are used as the impregnation substrate, a desired number of spread fibers may be formed into a sheet-like carbon fiber layer extending in the width direction, and a thermoplastic resin film may be superposed on at least one surface of the sheet-like carbon fiber layer to prepare a preform, which may then be hot-pressed. The fiber weight of the carbon fiber layer may be, for example, 40 to 250 g / m. 2 may be.

[0039] The width of the spread yarns may be about 1 to 30 mm. A desired number of spread yarns may be arranged in parallel in the width direction in accordance with the width of the thermoplastic resin film. The width of the thermoplastic resin film is not particularly limited, but can be 100 to 1000 mm or more.

[0040] During the heat pressing, molds may be placed on both sides of the preform, which is the object to be processed, in which the impregnated substrate and the thermoplastic resin film are stacked in the thickness direction, via release films. This makes it difficult for the thermoplastic resin film to adhere to the mold even when it melts.

[0041] The Vf value, which is the volume ratio of carbon fibers in the prepreg, is preferably 35% or more, and may be 50% or more. The Vf value is preferably 75% or less. If the Vf value is 75% or more, the resin cannot be sufficiently impregnated, which makes it easy for voids to occur, resulting in a decrease in the flexural modulus.

[0042] The prepreg of the embodiment can be used to manufacture a diaphragm by laminating it on at least one side of a foam. The prepreg may be laminated on both sides of the foam so that bubbles in the foam do not appear on both sides in the thickness direction of the diaphragm.

[0043] Preferred materials for forming the foam include resins such as polyethylene terephthalate (PET), polycarbonate (PC), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polystyrene (PS), polyimide (PI), polymethacrylimide (PMI), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyurethane (PU), and polyamide (PA). Of these, PS, PET, and PEI are preferred. The foam may be formed using one type of resin or two or more types in combination.

[0044] The method of foaming a resin to form a foam is not particularly limited, but examples include a method of supersaturating a resin with a gas, a method of blending a foaming agent into a resin, and a method of stretching a molded body in which a filler is filled into a resin to form gaps around the filler.The foaming agent may be a thermal decomposition type foaming agent that releases gas by thermal decomposition, or a volatile foaming agent that gasifies a low-boiling liquid by heating.Examples of the volatile foaming agent include organic compounds such as hydrocarbons and halogenated hydrocarbons.

[0045] The diameter of the cells contained in the foam is not particularly limited, but can be set appropriately within the range of, for example, 0.1 to 100 μm. The cells contained in the foam may be open cells or closed cells.

[0046] The thickness of the foam can be set as appropriate, for example, about 0.05 to 4.0 mm, and the thickness of the prepreg can be set as appropriate, for example, about 20 to 300 μm.

[0047] As a method for laminating the foam and the prepreg, the foam and the prepreg may be laminated together and the thermoplastic resin contained in the prepreg may be softened or melted by heat sealing, heat pressing, etc. This allows a sheet-like laminate having the foam and the prepreg to be produced.

[0048] When laminating foam and prepreg to form a diaphragm, a sheet-like laminate larger than the size of the diaphragm may be laminated and then molded to the size of the diaphragm. The diaphragm may be flat or may be molded into a three-dimensional shape such as a cone shape, a dome shape, or a horn shape.

[0049] When forming the diaphragm into a three-dimensional shape, the thermoplastic resin contained in the prepreg can be softened or melted to bond the laminate. Furthermore, a mounting portion for attaching the diaphragm to an acoustic device such as a speaker may be integrally formed. The mounting portion may be bent or molded in a different direction from the main body of the diaphragm.

[0050] The diaphragm of the embodiment can be used in acoustic devices such as speakers and microphones. In a speaker, to convert an electrical signal into a sound wave, a voice coil through which a current containing the electrical signal flows and a magnet (permanent magnet) may be combined with the diaphragm. By transmitting the vibration of the voice coil to the diaphragm, the sound expressed by the electrical signal is reproduced in the air.

[0051] The diaphragm of the embodiment is easily miniaturized and therefore suitable for acoustic equipment for electronic devices such as mobile phones, smartphones, personal computers, and portable terminal devices. Because the acid-modified polypropylene has high heat resistance, performance degradation can be suppressed even when the inside of the electronic device becomes hot. Since the components of the electronic device can be arranged at high density, the electronic device can be miniaturized.

[0052] The acoustic device of the embodiment can also be suitably used in transportation equipment such as automobiles, voice-operated devices, industrial equipment, household appliances, and the like.

[0053] The present invention has been described above based on preferred embodiments, but the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention.

[0054] Because acid-modified polypropylene has excellent adhesive properties to various resins and metals such as aluminum, the prepreg of the embodiment can be used for various adhesive applications. Because the matrix resin impregnated into the carbon fiber is a thermoplastic resin and does not have thermosetting properties, the prepreg has excellent storage stability. Because the prepreg does not have tack (adhesion) when cooled to room temperature, it also has good handleability.

[0055] Furthermore, since the prepreg of the embodiment is a thermoplastic prepreg in which carbon fibers are impregnated with a thermoplastic resin, the carbon fiber reinforced plastic (CFRP) obtained by molding the prepreg becomes a carbon fiber reinforced thermoplastic resin (CFRTP) because the matrix resin does not thermoset and maintains its thermoplasticity. Since the matrix resin remains thermoformable even after molding, it is easy to perform a thermoforming process such as heat pressing two or more times.

[0056] The carbon fiber used as the impregnation base material for the prepreg is continuous, which allows for the electrical conductivity of the carbon fiber to be utilized. Carbon fiber also has excellent mechanical strength, making it suitable for use as a structural material. [Example]

[0057] The present invention will be specifically described below with reference to examples.

[0058] Acid-modified polypropylene (melting point 140°C) was molded into a film as a thermoplastic resin and layered with carbon fiber (CF) UD (unidirectional) material (CFUD) to produce a preform. The preform was placed in a heat press, held at 170°C for 10 minutes, and heated and pressurized at a pressure of 1 MPa. This produced the prepreg of the example.

[0059] The flexural strength and flexural modulus of the prepreg of the example were measured in accordance with JIS K7074 (bending test method for carbon fiber reinforced plastics), and the flexural strength was 645 MPa and the flexural modulus was 152.7 GPa.

[0060] The carbon fiber volume fraction Vf value of the prepreg of the example was measured in accordance with JIS K7075 (testing method for fiber content and void content of carbon fiber reinforced plastics) and was found to be 48.5%.

[0061] When the flexural modulus of the carbon fiber (425 GPa) is Ef, the flexural modulus of the prepreg of the example (152.7 GPa) is Ep, and the Vf value of the example is 0.485, the elastic modulus expression rate was calculated using the formula (Ep / Ef) × (100 / Vf) (%). The elastic modulus expression rate of the prepreg of the example was 74%. [Explanation of symbols]

[0062] 1...foam, 2...prepreg, 3...diaphragm.

Claims

1. A prepreg having carbon fibers and an impregnated resin, the impregnating resin is a thermoplastic resin containing acid-modified polypropylene, A prepreg characterized in that the carbon fiber is a cloth (woven) material.

2. 2. The prepreg according to claim 1, wherein the thermoplastic resin contains 40% by weight or more of acid-modified polypropylene.

3. 3. The prepreg according to claim 1, wherein the carbon fibers have a diameter of 5 to 18 μm.

4. The carbon fiber has a fiber weight of 40 to 250 g / m ２ 4. The prepreg according to claim 1, wherein the carbon fiber layer is formed of:

5. 5. The prepreg according to claim 1, wherein a Vf value, which is a volume ratio of the carbon fibers in the prepreg, is 35% or more.

6. The prepreg according to any one of claims 1 to 5, wherein the prepreg is a prepreg for a diaphragm.

7. A diaphragm comprising a foam body and a prepreg according to any one of claims 1 to 6 laminated on at least one surface thereof.

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